(a) Field of the Invention
The present invention relates to an improved control circuit of rotational speed of a fan, and more particularly to an improved circuit of a control unit which provides a working voltage to a load unit, using a change in a period of sampling pulse output from a PWM (Pulse Wide Modulation) unit to enable the load unit to efficiently perform an adjustment, thereby facilitating an adjustment of speed and brightness to a fan device and a lamp device.
(b) Description of the Prior Art
Referring to FIG. 1 and FIG. 2, a conventional control unit A1 of a control circuit A of rotational speed of a fan is composed of an SSR (Solid State Relay) circuit A2 which includes an input circuit A21, a coupler A22, and an output circuit A23. As the circuit is complex, the cost is correspondingly high. However, as there is still a small amount of current flowing through the SSR circuit A2 when it is cutoff, hence a working voltage output to a load unit A3 cannot efficiently adjust the speed of fan. Moreover, a reaction speed of the SSR will not be enough if a period of sampling pulse is getting shorter; causing that only an incandescent lamp can be used.
Accordingly, how to eliminate the aforementioned problems is a technical issue which needs to be solved by the inventor.
Shortcomings of a conventional application
(1) The circuit is complex; hence its cost is high.
(2) It cannot efficiently achieve an effect of adjustment.
(3) When the sampling period is short, only the incandescent lamp can be used, thereby restricting the application.